Expanded Polypropylene foams are used in energy-absorbing applications, yet their mechanical response exhibits complex rate-dependency, damage, and permanent set, making accurate constitutive modeling challenging. This work proposes and validates a two-network viscoplastic model to describe the large-deformation compressive behavior of Expanded Polypropylene foams. The framework combines a hyperelastic network to capture the instantaneous nonlinear elastic response with a parallel viscoplastic network governed by an overstress flow rule to account for rate-sensitive effects. Model parameters were calibrated using experimental data from uniaxial compression tests at low (4.5 mm/min) and high (450 mm/min) rates. The model’s predictive capability was then assessed against an independent dataset at an intermediate rate (45 mm/min), achieving a coefficient of determination exceeding 0.98. Furthermore, an analysis was performed to quantify uncertainty, showing that the 95% confidence intervals and 95% prediction intervals for the stress response successfully encompassed the experimental validation data. The framework also provided an accurate approximation of key energy absorption parameters, confirming its empirical adequacy.
Alejandro E. Rodríguez-Sánchez (Thu,) studied this question.